1. Field of the Invention
The present invention relates to the wheel speed sensor mounting structure. More particularly, to the wheel speed sensor mounting structure where a pulsar ring that constitutes a part of the wheel speed sensor is rigidly mounted on a wheel by fastening together with a brake disc. The pulsar ring is hardly deformed even when the brake disc is thermally deformed due to special braking.
2. Description of Background Art
A brake disc for a disc brake and a pulsar ring that constitutes a part of a wheel speed sensor are known wherein the members are mounted on a wheel of a motorcycle or the like by fastening.
The wheel speed sensor is provided for measuring a wheel speed that is necessary for controlling an ABS (Antilock Brake System) or the like. The wheel speed sensor includes a pulsar ring that is rotated integrally with a wheel, and a sensor body portion that generates pulse signals corresponding to a rotational speed of the pulsar ring.
A conventional example of a motorcycle that mounts such a pulsar ring thereon is disclosed, for example, in JP-A-2010-270888. In this conventional example, a brake-use brake disc and a pulsar ring are fixed to a wheel of a motorcycle by fastening the brake disc and the pulsar ring together to a boss mounted on spokes. The brake-use brake disc is fastened to the boss by way of a stepped collar. A disc spring for a floating mount is arranged between the stepped collar and the brake disc. An accommodation recessed portion for accommodating a bolt head therein is formed on the stepped collar so as to prevent the bolt head of the bolt that fastens the brake disc and the pulsar ring together from largely projecting outwardly.
Due to such a construction, both the brake disc and the pulsar ring can be mounted on the wheel in a compact size.
Further, by adopting the above-mentioned floating mount, a stable positional relationship can be maintained between the sensor body portion and the pulsar ring.
More specifically, the brake disc is raised to a high temperature due to friction generated between the brake disc and a brake caliper at the time of braking a vehicle so that the brake disc is thermally expanded. Due to such thermal expansion, the brake disc is deformed so that the pulsar ring that is fastened to the wheel together with the brake disc is also deformed. As a result, there exists a possibility that the positional relationship between the sensor body portion that is fixed to a vehicle body side and the pulsar ring that is mounted on a wheel side in an integrally rotatable manner is changed.
However, due to the above-mentioned floating mount structure, only the brake disc simply extends in the radial direction and the pulsar ring is not deformed by thermal expansion of the brake disc. Thus, a stable positional relationship can be maintained between the sensor body portion and the pulsar ring.
This maintaining of the stable positional relationship is required for maintaining high wheel-speed detection accuracy.
Further, as shown in FIG. 10 and FIG. 11, a known the brake disc fastening structure is illustrated where a brake disc and a pulsar ring are rigidly mounted on a wheel without adopting the above-mentioned floating mount structure. The rigid mount structure is required for reducing the number of parts and for realizing the reduction of cost compared to the floating mount structure. In FIG. 10, a disc-brake-use brake disc 104 and a pulsar ring 120 are fixed to a wheel 101 of a motorcycle in a state where the brake disc 104 and the pulsar ring 120 are fastened together to a boss 150 that is formed on spokes 108. The brake disc 104 includes an annular braking portion 104a and a brake-disc-side mounting portion 104b that are formed on an inner peripheral portion of the braking portion 104a. Through holes 140 are formed in the brake-disc-side mounting portion 104b. 
FIG. 11 is a perspective view of the pulsar ring 120. The pulsar ring 120 includes a portion 121 that is detected by a sensor body portion 131, and pulsar-ring-side mounting portions 123 that project in the radially outward direction from an outer peripheral portion of the portion to be detected 121. Detection holes 122 are formed in the portion to be detected 121 over the whole circumference equidistantly. A flange 126 that is bent inwardly at an approximately right angle is integrally formed on an inner-peripheral-side edge portion of the portion to be detected 121. The flange 126 is continuously formed over the whole circumference of the portion to be detected 121.
The pulsar-ring-side mounting portion 123 is bent at a root portion 123a where the pulsar-ring-side mounting portion 123 is joined to the portion to be detected 121 thus forming an inclined portion 123b that extends inwardly, that is, in the direction toward the center of rotation C in an inclined manner. The inclined portion 123b is folded back in the radially outward direction at an outer folded-back portion 123c thus forming a seat portion 125, and a through hole 124 is formed in the seat portion 125. A position of the seat portion 125 is arranged further inside in the direction toward the center of rotation C than a position of a distal end of the flange 126.
The flange 126 plays a role of increasing the rigidity of the whole pulsar ring 120 to a relatively high value together with the pulsar-ring-side mounting portions 123 having the bent structure.
Then, the seat portion 125 is placed on an end surface of the boss 150, the brake-disc-side mounting portion 104b of the brake disc 104 overlaps with the seat portion 125, the through holes 124, 140 are aligned with threaded holes 151 formed in the boss 150, and the stepped bolts 110 are fastened to the boss 150. Thus, the brake-disc-side mounting portion 104b and the pulsar-ring-side mounting portion 123 are fixed together to the boss 150 by fastening and thereby are rigidly mounted on the boss. The portion to be detected 121 is arranged close to a sensor body portion 131 with a predetermined distance therebetween so that when the portion to be detected 121 is rotated, the detection hole 122 passes an area close to a distal end of the sensor body portion 131.
To consider the case where the above-mentioned rigid mount structure is adopted, in a normal braking operation that is assumed in general traveling, the brake disc 104 is raised to a high temperature (for example, approximately 450° C.) due to friction heat generated mainly at a friction portion thereof with a brake caliper, and thermally expands. Accordingly, the seat portion 125 of the pulsar-ring-side mounting portion 123 is pulled in the radially outward direction by way of the bolt 110. However, as described above, the pulsar ring 120 as a whole has relatively high rigidity. Thus, the pulsar ring 120 can withstand a tensile force that is usually assumed to be generated without being deformed.
Accordingly, the positional relationship between the portion to be detected 121 and the sensor body portion 131 is maintained within a predetermined range even in a rigid mounting state.
On the other hand, at the time of performing a special braking operation, for example, under a special braking state where the brake disc 104 is raised to an extremely high temperature (for example, approximately 600° C. or above) due to extremely continuous braking or the like, there may be a case where the pulsar ring 120 that is rigidly mounted by fastening together with the brake disc 104 is deformed by the thermal expansion of the brake disc 104.
More specifically, when the brake disc 104 that is raised to an extremely high temperature under such a special braking state is largely thermally deformed by the thermal expansion, a large tensile force directed in the radially outward direction is applied to the bolt 110 from the brake disc 104. Accordingly, in the pulsar ring 120 that is rigidly mounted by fastening together with the brake disc 4 using the bolt 110, the seat portion 125 is strongly pulled in the radially outward direction indicated by an arrow A in FIG. 11.
Such a large tensile force acts on the portion 121 from the pulsar-ring-side mounting portion 123 and intends to increase a diameter of the portion 121 to be detected. However, the portion 121 has high rigidity due to the flange 126 formed on the inner-peripheral-side edge portion thereof. Thus, as shown in an enlarged portion in FIG. 11, a resistance force against such a tensile force is generated in an inner peripheral portion of the portion to be detected 121 in the opposite direction, that is, in the radially inward direction as indicated by an arrow D. Further, there exists a difference h in height between the portion to be detected 121 and the seat portion 125 of the pulsar-ring-side mounting portion 123 due to the inclined portion 123b. Thus, the portion 121 to be detected is positioned in an offset manner with respect to the seat portion 125. Accordingly, as indicated by an arrow B, the portion to be detected 121 is twisted due to the bending deformation that makes the portion to be detected 121 inclined inwardly in the direction toward the center of rotation C and thereby a large tensile force generated by the thermal deformation of the brake disc 104 that is raised to an extremely high temperature under a special braking state is absorbed.
When such twisting is generated in the portion to be detected 121, the portion 121 is separated from the sensor body portion 131. Thus, there arises a possibility that the positional relationship between the sensor body portion and the portion to be detected 121 falls outside a predetermined range.
However, in maintaining the high wheel-speed detection accuracy of the wheel speed sensor 130, the positional relationship between the sensor body portion 131 fixed to a vehicle body side and the portion to be detected 121 of the pulsar ring 120 mounted on a wheel 101b side in an integrally rotatable manner is important. Accordingly, there may be a case where it is necessary to maintain such a positional relationship within the predetermined range even under such a special state.